1. Field of the Invention
The present invention relates to a camera that carries out photographing by capturing object light entered via a photographing optical system.
2. Description of the Related Art
Cameras have hitherto been known which comprise a photographing optical system having a variable focal distance, e.g. a zoom lens to take a photograph on a photograph film. A camera comprising a zooming lens uses a so-called zooming function that varies a magnifying power by varying a focal distance to enable more variable framing than a camera comprising a single focus lens, e.g. enable a far object to be photographed as a larger image than the latter.
The maximum aperture of a camera comprising a zoom lens is determined, when the camera is designed, on the basis of the focal distance measured when the zoom lens is set to use a long focal distance as well as an F value of the zoom lens. However, if the zoom lens of the camera is set to use a short focal distance, when a photograph is taken with the diaphragm opened so as to obtain the maximum aperture, the quantity of light in peripheral portions of the angle of view of the photograph decreases compared to a central portion thereof, so that peripheral portions of the resulting photograph, notably the four corners thereof appear dark. It is known that the decrease in quantity of peripheral light can be resolved by reducing the aperture of the open diaphragm by about one or two levels.
Thus, for a camera comprising a zoom lens, a decrease in quantity of peripheral light is resolved by employing a diaphragm comprising an aperture regulating mechanism that regulates the aperture to a value smaller than the above described maximum value if the zoom lens is set to use a short focal distance.
In general, with a camera comprising a photographing lens with a focal distance of about 30 mm, a shutter speed of {fraction (1/30)} second is said to be the lowest shutter speed at which photographing can be achieved without using any fixture such as a tripod, i.e. without being affected by image shakes.
However, with the camera comprising the diaphragm aperture regulating mechanism, to prevent a decrease in quantity of peripheral light described above, the zoom lens is set to use a short focal distance to regulate the aperture of the diaphragm to a value smaller than the maximum value, so that when a photograph is taken in a dark place, the photograph appears dark. In this case, to obtain a brighter photograph, the shutter speed may be reduced. However, when the shutter speed is reduced to shorter than {fraction (1/30)} second, a fixture such as a tripod is required to prevent image shakes.
In view of these circumstances, it is an object of the present invention to provide a camera that can take a bright photograph in a dark place.
To attain the above object, the present invention provides, according to a first aspect thereof, a camera comprising a photographing optical system having a variable focal distance and a diaphragm having a maximum aperture regulated, in response to the photographing optical system being set to use a predetermined focal distance or shorter, to a second value smaller than a first value used when the photographing optical system is set to use a predetermined long focal distance, the camera carrying out photographing by capturing object light entered via the photographing optical system and the diaphragm, the camera further comprising:
a photometric section that measures a light value; and
a diaphragm restriction clearing section that clears an aperture regulation for the diaphragm and sets the aperture of the diaphragm at a value within a range between the first maximum value and the second maximum value depending on the light value measured by the photometric section, the range including the first maximum value itself, if the light value measured by the photometric section is equal to or smaller than a predetermined value.
In general, if a photograph is taken in a dark place, e.g. a night view is photographed, a decrease in quantity of peripheral light does not substantially affect the resultant photograph. The present invention is completed in view of this point. If the light value is equal to or smaller than a predetermined value, the aperture regulation is cleared, and the aperture of the diaphragm is set at a value within a range between a maximum value obtained when the photographing lens is set to use a predetermined long focal distance and a second maximum value smaller than the first maximum value, depending on the light value measured by the photometric section, the range including the first maximum value itself. Accordingly, a camera is implemented wherein when a photograph is taken in a dark place where a decrease in quantity of peripheral light does not affect the resultant photograph, a bright photograph can be taken without using any fixture.
In this case, the diaphragm restriction clearing section may set the aperture of the diaphragm at the first maximum value when the aperture regulation for the diaphragm is cleared.
When the aperture is set at the first maximum value, no mechanisms are required which regulate the aperture to a value between the first maximum value and the second maximum value. Consequently, the structure of the diaphragm is simplified.
In a preferred aspect, the diaphragm restriction clearing section clears the aperture regulation for said diaphragm if the light value measured by said photometric section is equal to or smaller than a predetermined value set equal to or smaller than LV6.
Thus, the light value at which the aperture regulation for the diaphragm is cleared is preferably set equal to or smaller than LV6, which is smaller than that obtained when a photograph is taken indoors.
Further, preferably, the camera has a photosensitized material loaded therein to take a photograph on the photosensitized material.
The present invention focuses on the fact that photographing of a night view is not affected even by the aperture of the diaphragm with which a decrease in quantity of peripheral light is noticeable when a photograph is taken in a well lighted place. For a digital camera, image processing may be used to correct the decrease in quantity of peripheral light on image data after photographing. However, for a camera of a type that takes a photograph on a photosensitized material, the decrease in quantity of peripheral light cannot be corrected. Therefore, the present invention is suitable for a camera of a type that takes a photograph on a photosensitized material. However, even for a digital camera, application of the present invention eliminates the need to take trouble to correct the decrease in quantity of peripheral light by image processing.
To attain the above object, the present invention provides, according to a second aspect thereof, a camera comprising a photographing optical system and a diaphragm which is opened so as to obtain a predetermined first maximum aperture and which has the maximum aperture regulated to a predetermined second value smaller than the first value, the camera carrying out photographing by capturing object light entered via the photographing optical system and the diaphragm, the camera further comprising:
a photometric section that measures a light value; and
a diaphragm restriction clearing section that clears an aperture regulation for the diaphragm and sets the aperture of the diaphragm at a value within a range between the first maximum value and the second maximum value depending on the light value measured by the photometric section, the range including the first maximum value itself, if the light value measured by the photometric section is equal to or smaller than a predetermined value.
According to the camera according to the second aspect, if the light value measured by the photometric section is equal to or smaller than a predetermined value, the aperture regulation for the diaphragm is cleared and the aperture of the diaphragm is set at a value between the first maximum value and the second maximum value smaller than the first maximum value depending on the light value measured by the photometric section. Consequently, when a photograph is taken in a well lighted place, the quantity of peripheral light is reduced. On the other hand, when a photograph is taken in a dark place, the range in which a bright photograph can be taken is increased without using any fixture.